DESCRIPTION (Applicant's Description) There is considerable evidence that diet plays a role in prostate cancer. In addition to increased risk with a diet high in fat, dietary lycopene has emerged as a possible protective factor from a recent cohort study, and selenium and vitamin E have emerged as possible protective factors from recent randomized trials. However, these three micro nutrients were not hypothesized a priori to be related to prostate cancer, so those findings are best regarded as only hypotheses to be tested in other studies. Assaying nutrients in stored serum samples from defined cohorts is a useful approach to studying etiologic factors in cancer. This is a proposal to conduct a nested case-control study of serum samples stored by freezing following PSA screening for prostate cancer during the national Prostate Cancer Awareness Week in September, 1995. The stored serum samples from men subsequently diagnosed as having prostate cancer (cases) will be matched by age, race, and clinic site to an equal number of samples from men who had both normal rectal exams and normal PSA levels (controls). The follow-up of the 1995 screening cohort is still underway, but we estimate at least 200 cases will have had stored serum samples. The serum will be assayed, blinded to case-control status, at the Nutritional Biochemistry Laboratory at CDC in Atlanta for carotenoids, vitamin E, and selenium. The analysis will include stratification by age, race, PSA level, symptomatology, and tumor volume. This study will provide timely new information regarding the possible importance of lycopene, vitamin E, and selenium in the prevention of prostate cancer.